Method and device for the production of slush from liquefied gas

ABSTRACT

A method for producing slush from liquefied gas wherein solid crystals are formed and mixed with the liquefied gas to produce slush. The solid crystals are produced from liquid particles which are released into or enter a gas atmosphere under pressure, wherein the temperature of the gas atmosphere is below the freezing point of the liquid particles. A device is also provided for producing the slush from liquefied gas in a cryostat container which is partly filled with the liquefied gas which mixes with the solid crystals to produce slush. The device has an atomizing device for producing the liquid particles from the liquefied gas supplied to it. The liquid particles enter a gas atmosphere which exists above the liquefied gas in the container.

The object of the invention relates to a method for producing slush fromliquefied gas, by which solid crystals are formed and mixed or are mixedwith the liquefied gas to produce slush. The invention also relates to adevice for producing slush from liquefied gas.

Hydrogen (H₂) is suitable as fuel due to its light molecular weight andits high degree of combustion heat for highly energetic rocketpropellant combinations as fuel. Liquid hydrogen (LH₂) belongs to thecryogenic fuels and requires that the tanks be appropriatelyheat-insulated if applied in a motive power unit. Special safetymeasures must be taken when handling hydrogen. The danger of explosionby hydrogen is greater than in the case of other fuels because of itshigh diffusion velocity. Even small sparks (e.g. by static charge) issufficient to cause a fire or an explosion.

Due to the requirements for space transport systems to be constructed tosave weight and space, gas liquefaction and further compression of theliquid hydrogen at a low temperature was considered for storage of thedriving gas, hydrogen. It was finally proposed to apply slush—withhydrogen crystals mixed with liquid hydrogen, having a crystal contentof 40-60% by weight. Slush has a number of favourable characteristics,like high density, high cold content and flows well. Due to thesecharacteristics the slush of liquefied gases is extremely suitable as acryogenic refrigerating agent not only for space missions but also forterrestrial application.

Methods have already been developed by which hydrogen slush can beproduced. The freezing-thawing technology and the Auger methods whichhave been described in different ways in literature also belong to thesemethods.

In the freezing-thawing technology, liquid hydrogen which is cooled downto triple point level, is vaporized by creating a vacuum, by whichhydrogen crystals are formed on the surface of the liquid hydrogen. Thevacuum pressure undergoes cyclic changes to values slightly above andslightly below the triple point pressure, by which a movable matrix ofhydrogen crystals forms at a pressure which is below the triple pointpressure. Hydrogen condenses on the crystals at a pressure that isslightly above the triple point pressure and the solid particles sinkinto the liquid. A certain advantage of this method is the relativesimplicity of the required technical equipment. However, since the slushproduction is achieved at underpressure when this method is applied,there is a certain safety risk because an unintentional suction of air,thus the formation of an explosive hydrogen-oxygen mixture should beexpected. The production quantity is also limited, perhaps due to thecooling process of the liquid hydrogen which is either achieved by thevaporization of a given quantity of liquid hydrogen via indirect coolingby means of injecting cold helium or by means of a gaseous mixture ofhelium-neon. The required large quantities of at least some tons per daycould not be achieved according to this method up to now because of thecommercial expenses involved. To improve the quality of the hydrogenslush also necessitates an aging process of one to two days.

In the case of the second indicated method for producing hydrogen slush,the Auger method, a hollow cylinder filled with helium gas and placed inliquid hydrogen is cooled down to a temperature below the freezing pointof the hydrogen. The design enables the formation of solid hydrogen onthe inner walls of the cylinder, which is constantly scraped off bymeans of a swiveling spiral. At the bottom part of the device, thehydrogen crystals which are formed by that method mixes with the liquidhydrogen to slush.

This procedure has the advantage over the freezing-thawing method thatthe safety risk involved is not given in this case because there is nounderpressure. However, it was only possible to apply this method up tonow only for the production of quantities for the laboratory. A devicewhich is appropriate for the industrial production of slush according tothis method would hardly be able to be realized because of the requiredmechanical efforts and the costs involved. The slush produced accordingto this method must also undergo an aging process of one to two days inthe long run.

The aim of the invention is now to develop a method for producing slushfrom liquefied gases, especially for producing hydrogen slush, by whichthe application of underpressure can be avoided and by which even largerquantities of slush can be produced. Apart from that it should also bepossible to improve the quality of the forming slush so that, forinstance, the duration of the aging process of the slush can be reducedand the flowing quality of the forming slush in the lines, valves, etc.can be improved. The aim of the invention is also to develop a devicewhich is appropriate for the application of this method, safe to operateand to produce slush according to the industrial standards, with whichthe aims indicated can also be achieved with as little mechanical effortas possible.

The invention solves these tasks by solid crystals being formed fromliquid particles which are released or admitted under pressure to a gasatmosphere, which has a temperature which is below freezing point of theliquid particles.

The method according to the invention thus ensures freezing orcrystalizing of the particles in a relatively short space of time.Therefore, the forming solid particles have more of a round shape andthere is a good quality of slush at increasing density. Due to the roundshape either no or a slight aging process is necessary in order toensure a high density of the slush and good flowing. No underpressure isrequired for producing the slush so that safety risk is reducedextremely in case hydrogen slush is produced.

According to another feature of the invention, the liquid particles areformed in a special and simple way by atomization of the liquefied gas.

For this process only an appropriate atomizing device device is requiredwhich can be mounted in a simple manner and consists of at least anozzle or a centrifugal and mixing chamber or similar.

The atomization process can be effected in a simple manner at leastpartly by gas being supplied to the atomizing device under pressurewhich preferably is according to the gaseous phase of the suppliedliquefied gas.

Therefore the liquefied gas supplied to the atomizing device can becooled down before and/or during the atomizing process by means of agaseous cooling medium. Additional cooling-down shortens the period ofcrystalization.

The method can be designed in such a way that either additionally oralternatively to atomization and by applying a supplied gas which ispressurized, atomization can be effected at least partly when theliquefied gas discharges into the cold gas atmosphere.

In order to ensure atomization which is as optimum as possible, i.e.bursting of the liquid jet discharging from the atomizing device, thepressure in the cold gas atmosphere is set at a rate which is below thecorresponding critical pressure at the discharge aperture of theatomizing device.

In order to minimize the safety risk, the pressure in the cold gasatmosphere where crystalization occurs is set in such a way so that itcorresponds at least to the ambient air pressure, it will particularlybe at a value that is slightly above the ambient air pressure.

The inventive method has the special advantage that the forming slushcan be continuously drained off essentially during the production of newslush. For this process it is favourable if draining-off of the slush iscontrolled by constant measurement of its density, which ensures thesame quality of the drained slush.

The inventive method is especially suitable for producing hydrogen slushwhich has become more important as cryogenic fuel.

In this case helium gas is suitable as a cooling medium which is to besupplied to the atomizing device.

There is an advantage when a helium gas atmosphere, which can be madeavailable at a corresponding low temperature, is applied as a cold gasatmosphere where the liquid particles freeze or crystalize.

The present invention also relates to a device for producing slush fromliquefied gas using a cryostat container, which is partly filled withliquefied gas that mixes with solid crystals to produce slush. Theinventive device is characterized by an atomizing device arranged in thecryostat container for forming liquid particles from supplied liquefiedgas. This device discharges the liquid particles above the gas in thecontainer into a gas atmosphere, which has a temperature below thefreezing point of the liquid particles.

The inventive device thus ensures in a simple manner that crystals canform in a relatively short space of time, which ensures a high qualityof slush.

The atomizing device can be mounted simply and consists of at least anozzle or a centrifugal and mixing chamber or similar.

In order to ensure atomization of the supplied liquefied gas, differentpossibilities are available. There is one design that is especiallysimple by which the atomizing device has a supply line for thepressurized gas which thus effects atomization within the atomizingdevice.

In another design, the discharge aperture of the nozzle of the atomizingdevice is designed in such a way so that the set pressure there ishigher than that in the cold gas atmosphere outside of the pressure ofthe atomizing device. In this type of design, the jet can burst whendischarging out of the atomizing device thus causing an optimumturbulence of the forming liquid particles.

In order to maintain the crystalization period as short as possible, theatomizing device can have another supply line for a gaseous coolingmedium. In case of a design with a centrifugal or mixing chamber, thesupply of a cooling medium in the atomizing area is especiallyprofitable.

In a preferable design of the atomizing device, the gaseous coolingmedium is supplied in a pressurized state by means of gas nozzles andthen led into the atomizing device in a gas guide cone which forms adischarge gap in the area of the nozzle. In this design the gas jet isnot only a cooling medium, it also contributes to a turbulence of theliquid particles and the forming crystal particles discharging from thenozzle.

In order to ensure as far as possible that there is a constant cold gasatmosphere in the cryostat container, it is of an advantage, if thecontainer has a number of inlets for supplying the gas which forms thecold gas atmosphere. These inlets shall be specially arranged as asprinkler. This also enables a quick desired change of pressure.

A continuous production of slush is possible with the invention becauseit can be provided with devices to drain off the forming slush and tosupplement the quantity of liquefied gas during the manufacturingprocess. In order to ensure the good quality of the drained slush, thedevice is equipped with a system for measuring the density of the slushwhich controls draining of the slush.

The device can be profitably applied to produce hydrogen slush fromhydrogen.

In this case the pressurized gas supplied for atomization within theatomizing device will be hydrogen which will be also an advantage.

Helium gas is especially suitable in this case as cooling medium for thesupplied liquid hydrogen.

Helium is also especially suitable for the cold gas atmosphere withinthe cryostat container because it ensures the required low temperatures.

The invention can be developed into a production plant directly, withwhich the larger quantity of slush can be produced. It can be equipped,for example, with a number of atomizing devices which can be connectedas a ring or similar.

Further features, advantages and particulars of the invention will nowbe shown and described in detail in the diagram which present examplesof the design of the device. FIG. 1 shows an intersection by a simplydepicted invention for producing slush from liquefied gas, by which theinvention is described on the basis of the production of hydrogen slush,FIG. 2 a possible basic design of the atomizing device shown in FIG. 1,FIG. 3 another somewhat concrete design of an atomizing device in alongitudinal cross-section and FIG. 4 a top view of a possiblearrangement of a number of atomizing devices for a medium-sizedproduction plant.

In case of the invention for the production of slush, here especiallythe production of hydrogen slush, it relates to a special spray method,by which the solid crystalized portion of the slush forms from theatomized particles of liquid hydrogen. A gaseous medium is preferred forthe atomization of liquid hydrogen, e.g. gaseous hydrogen, set under ahigher pressure, by which the stream of the atomized hydrogen particlesenters into a cold (approx. 11 k) helium gas atmosphere and expands.Solid hydrogen crystals form there which settle on the surface of theliquid hydrogen (triple point hydrogen, 13.8 k) in the system and thensinks into it. During this process hydrogen slush forms with anincreasing portion of crystalized particles and thus at increasingdensity and quality.

The diagram in FIG. 2 shows various possibilities of the design ofatomization, applying the invention, atomizing device 2.

Liquid hydrogen (LH₂) is supplied to atomizing device 2 in theconvergent trumpet-shaped cross-section and transported to isolatednozzles which are arranged in the area of the orifice and which have notbeen illustrated here. Gaseous helium (GHe) is supplied in the requiredquantity as cooling medium. Pressurized gaseous hydrogen (GH₂) issupplied by means of supply line 2 a before the area of the orifice ofatomizing device 2, by which liquid hydrogen at least partly atomizes.Extensive and complete atomization can be achieved by adequate controlof pressure and quantity of the gaseous hydrogen. Instead of gaseoushydrogen or in addition to this, gaseous helium can also be applied foratomization by means of another supply line 2 b. At the same timegaseous helium cools down the forming particles. The forming hydrogenparticles (H₂ particles) expand after discharging from the nozzle intothe cold helium gas atmosphere and freezes there so that hydrogencrystals are formed.

Crystalization requires only a short space of time so that the shape ofthe forming particles are mostly round. This favourably influences thequality of the forming slush, e.g. its flowability, and requires eitherno or only a short aging process of the forming slush.

The liquid hydrogen (LH₂) which is supplied to the nozzle can besupplied in any liquid state which is between its state as NBPLH₂(normal boiling point liquid hydrogen 20 k, 1 bar) and its state asTPLH₂ (triple point liquid hydrogen 13.8 K, 0.07 bar).

Atomization of liquid hydrogen (LH₂) can be achieved according to thedesign of atomizing device 2 and when the pressure ratio is setaccordingly, at least partly, and during discharging out of the nozzle,by bursting of the hydrogen jet when discharging out of the nozzle. Inthis way there is an optimum turbulence of the hydrogen particles in thehelium gas atmosphere. This “bursting” is achieved by dropping ofpressure in the helium gas atmosphere below the corresponding criticalpressure of the discharge aperture of the nozzle. During this processatomization can take place entirely during discharging out of the nozzleif the nozzles are appropriately designed, especially the cross-sectionsurface at the discharge, and further parameter, like the pressureratio.

FIG. 3 shows another possible and somewhat concrete example of a designof an invented atomizing device 12. Atomizing device 12 comprises ahousing 13, which consists of a special cylindrically designed basicpart 13 a and a frustum-shaped gas conducting piece 13 b, between whichthere is an intermediate piece 13 c, a type of plate. The cryogenicliquid to be atomized, here liquid hydrogen, is supplied via line 14 ofatomizing device 12 and directed in the internal part of the housing 13via a nozzle carrier 15 to nozzle 15 a, where bursting of the jet occursdue to the hypercritical discharge.

Nozzle 15 a is located in the area of the upper narrow end of thefrustum-shaped gas conducting part 13 b which is not closed, but formsdischarge gap 16 between nozzle 15 a or nozzle carrier 15 and the upperhousing edge.

Basic part 13 a of housing 13 forms a ring channel for cooling gasaround line 14 or nozzle carrier 14 which is directed under pressure viaanother line 17 into the channel. The cooling gas in this case isespecially gaseous helium (GHe) which has a temperature lower than thatof the cryogenic liquid.

The cooling gas is pressed from the ring channel in basic part 13 a viaa number of gas nozzles 18 into the internal part of the frustum-shapedgas conducting part 13 b and streams there towards discharge gap 16where it encloses the liquid particle jet flowing out of nozzle 15 alike a cooling jacket. The gas jet also contributes to additionalturbulence of the liquid particles thereby.

Nozzle 15 a can be provided with a twist bore which also contributes toturbulence of the liquid jet. In addition a heating device 19, which canbe switched on as desired, can ensure that the cryogenic liquid does notfreeze within the area just in front of the discharge aperture of nozzle15 a.

Atomization of hydrogen can also be effected in the centrifugal ormixing chamber where gas for the atomization and also a cooling medium(helium gas) streams in. During this process particles are mixed withthe cooling medium and discharge out of the atomizing device at atemperature that is near to the freezing point.

The coldness that effects quick crystalization of the hydrogen particlesis now ensured on the one hand by expansion taking place duringdischarge and on the other hand by the temperature of the helium gasatmosphere in which the atomized hydrogen particles enter.

As mentioned it is favourable in this connection if cold helium gas isdirected into the atomizing device or the mixing chamber.

The hydrogen crystals which are formed in the helium gas atmosphere sinkon the surface of liquid hydrogen (TPLH2, 13.8 K, approx. 0.07 bar),mixes with the liquid hydrogen and is formed to slush together with itat increasing quality. An occasional mechanical mixing of the slush cancontribute to improving its flow quality.

Blending or mixing of the produced slush also prevents unintentionalcoagulation of same. As an alternative to blending, a helium gas streamwhich can be directed via gas nozzles into the slush or a heating devicecan be applied to prevent coagulation.

FIG. 1 shows a diagram of a basic design of a device that operatesaccording to the invention. The device comprises a cryostat container 1,the walls of which are insulated accordingly (vacuum insulation andsuperinsulation by special LN₂ radiation protection). At the upper partof container 1 a supply line for the gaseous helium, which will besupplied at a temperature of approx. 11 K, will be provided through thecover. The supply line discharges preferably in a type of ring channelfrom where helium gas can stream in via a number of orifices 3, like asprinkler.

At the bottom part of container 1 there is, as already mentioned, liquidhydrogen 4 through which atomizing device 2 is also directed. This hasthe advantage of additional cooling of atomizing device 2. Thecrystalization process can be monitored via window 5.

By means of the supplied gaseous helium, the pressure in container 1above the liquid hydrogen 4 or the forming slush is maintained slightlyabove 1 bar. This minimizes the safety risk because air cannot be suckedin through any leakages.

Furthermore a high pressure relief valve 6 can be provided which isactivated at a certain inner pressure of, for instance, 1.1 bar.

The length of time during which the hydrogen particles can be spun untilcrystalization in container 1 can be controlled by setting the pressureof the helium which streams in like a sprinkler. For this purpose anequilibrium can be set between the gaseous helium from the top and theGH₂/LH₂ stream which is at the bottom. At the bottom part of thecontainer there is an outlet 7 for the produced hydrogen slush (SLH₂),the production of which is constantly being increased. By monitoring andmeasuring the pressure of the formed slush, the discharged quantity canbe regulated. At the same time corresponding supply lines ensure, in away that has not been described, that liquid hydrogen is supplemented incontainer 1. According to this, a continuous production of slush ispossible. In this way even when handling the slush a simple and quickcompensation (replacement) of melted slush is ensured.

The invention also comprises a heat exchanger which is not illustrated.A heat exchanger will be provided to transform the existing medium inthe gaseous phase into the cryogenic liquid (e.g. LH₂) to be atomized,which is carried out with liquid helium (LHe) in the case of hydrogen.Another heat exchanger cools the warm gaseous medium (e.g. GHe) to coldgaseous medium, especially also by applying liquid helium (LHe). Thecold gaseous medium (e.g. GHe cold) is used on the one hand for theabove mentioned sprinkler and on the other hand as cooling gas for theatomizing device.

The device described in its basic construction can be developed into acomplete production plant for large quantities of hydrogen slush. Thisis simply possible, for instance, by connecting a number of atomizingdevices, e.g. ring-shaped, to one another.

FIG. 4 shows a top view of a very favourable arrangement from a numberof atomizing devices 12, in this case fifteen. The slush productionplant comprises a cylindrical supporting housing 20 which is especiallyvacuum-insulated and radiation-protected and in which two rings of theatomizing devices 12 are arranged in a concentric way. There arering-shaped supply lines 21 for the cryogenic liquid and the cooling gasprovided for each of these rings. A slush drainage which is notillustrated here can be provided to collect the produced slush.

Apart from the manufacture of hydrogen slush, the production of othertypes of slush from other liquefied gases can be achieved according tothe method of the invention and with the appropriate adapted devicesaccordingly, e.g. nitrogen, by which slush is applied as a cryogeniccooling agent during long transport periods, or even oxygen.

What is claimed is:
 1. A method for producing slush from liquefied gasby which solid crystals are formed which mix with the liquefied gas toproduce slush characterized by the release or admission to a gasatmosphere of pressurized solid crystals formed from liquid particleswhich has a temperature below the freezing point of the liquid particlesand the liquid particles being formed by atomization of the liquifiedgas.
 2. Method according to claim 1 characterized by atomization iseffected by means of an atomizing device (2, 12) which comprises anozzle (15 a), a centrifugal and mixing chamber.
 3. Method according toclaim 2 characterized by atomization is effected at least partly bymeans of a pressurized gas supplied to the nozzle (2), a centrifugal andmixing chamber.
 4. Method according to claim 3 characterized by this gasof the gaseous phase corresponding to the supplied liquefied gas. 5.Method according to claim 4 characterized by the liquefied gas suppliedto the atomizing device (2, 12) being cooled down before atomization bymeans of a gaseous cooling medium.
 6. Method according to claim 2characterized by atomization being effected at least partly at thedischarge of liquefied gas into the cold gas atmosphere.
 7. Methodaccording to claim 6 characterized by pressure in the cold gasatmosphere being set lower than the corresponding critical pressure inthe discharge aperture of the nozzle (15 a) of the atomizing device (2,12).
 8. Method according to claim 7 characterized by pressure in thecold gas atmosphere being set to at least the value of the ambient airpressure.
 9. Method according to clam 8 characterized by forming slushbeing drained off at least continuously during the production of newslush.
 10. Method according to claim 9 characterized by the slush thatis drained being controlled by means of constant measurement of thedensity.
 11. Method according to claim 10 characterized by the liquefiedgas being liquid hydrogen.
 12. Method according to claim 11characterized by the liquid hydrogen supplied to the atomizing device iscooled down by supply of helium gas.
 13. Method according to claim 12characterized by a helium gas atmosphere being the cold gas atmosphere.14. A device for producing slush from liquefied gas is a cryostatcontainer which is partly filled with liquefied gas which is mixed withsolid crystals to produce slush characterized by an atomizing device (2,12) for forming liquid particles from supplied liquefied gas to releasethe liquid particles above the liquefied gas in the container into thegas atmosphere which has an ambient pressure and a temperature below thefreezing point of the liquid particles wherein the liquid particles areformed by atomization of the liquefied gas.
 15. Device according toclaim 14 characterized by the atomizing device (2, 12) comprising anozzle (15 a), a centrifugal and a mixing chamber.
 16. Device accordingto claim 15 characterized by the atomizing device having a supply line(2 a) to supply pressurized gas.
 17. Device according to claim 16characterized by the discharge aperture of the nozzle (2) of theatomizing device being selected in such a way that the set pressurethere exceeds the pressure in the cold gas atmosphere outside of theatomizing device.
 18. Device according to claim 17 characterized by theatomizing device (2, 12) having at least one supply line (2 b, 17) tosupply a gaseous cooling medium.
 19. Device according to claim 18characterized by the atomizing device (12) having gas nozzles (18) tosupply the gaseous pressurized cooling medium.
 20. Device according toclaim 19 characterized by the atomizing device (12) having a gas guidecone (13 b) for the gaseous cooling medium which forms a discharge gap(16) in the area of the nozzle (15 a).
 21. Device according to claim 20characterized by the supply line of the gas forming the cold gasatmosphere having a number of inlets (3) which are especially arrangedlike a sprinkler.
 22. Device according to claim 21 characterized bydevices being provided for draining off the formed slush and tosupplement the quantity of the liquefied gas during the productionprocess.
 23. Device according to claim 22 characterized by having adevice for measuring the density of the slush with which the drainingoff of the slush is controlled.
 24. Device according to claim 23characterized by liquid hydrogen being the liquefied gas.
 25. Deviceaccording to claim 24 Characterized by hydrogen being the pressurizedgas which is supplied to the atomizing device.
 26. Device according toclaim 18 characterized by helium gas being the cooling medium. 27.Device according to claim 26 characterized by helium gas forming thecold gas temperature.
 28. Device according to claim 27 characterized byhaving a number of atomizing devices (12) which are arranged in acircular shape.